For many years now, telecommunications carriers have been deploying packet-switched networks in place of, or overlaid upon, circuit-switched networks for reasons of efficiency and economy. Packet-switched networks such as Internet Protocol (IP) or Ethernet networks are intrinsically connectionless in nature and, as a result, suffer from Quality of Service (QoS) problems. Customers value services which are guaranteed in terms of bandwidth and QoS.
It is desired to use Ethernet switches in carriers' networks. Use of Ethernet switches in carriers' networks would have the advantages of interoperability, since mappings between Ethernet and other frame/packet/cell data structures such as IP, Frame Relay are well known, and economy, since Ethernet switches are relatively inexpensive compared to IP routers, for example. It would also provide a distinct advantage of being the principal technology used by enterprises that require a wide area network service from a carrier and therefore able to work in a native mode.
A conventional high-capacity Ethernet switch has a set of input ports and a set of output ports which are connected via a switch fabric. On start-up, or on re-start, a conventional switched Ethernet network behaves like a ‘classic’ Ethernet Local Area Network (LAN) in that every Ethernet frame is broadcast across the entire network. Every switch, upon receiving an Ethernet frame on one port, broadcasts the frame out on every other port. The process repeats as the frame is received by other switches, thus broadcasting the frame across the entire network. In switched Ethernet networks Medium Access Control (MAC) address auto-learning functionality is provided to improve configuration efficiency. Ethernet frames have source and destination MAC addresses corresponding to their source and destination Ethernet ports. When an Ethernet frame sent out by a source switch is received by an intermediate or destination Ethernet switch the receiving switch observes the port on which the frame was received and the source address of the frame. The switch then builds a forwarding table for use in future frame switching. Once a MAC address has been seen on a port, that information is made available to all ports to be used if any encounters that address. A central processor builds a single Forwarding Database (FDB) on the basis of MAC addresses seen on all ports. Over time, the network builds up forwarding state enabling efficient switching of Ethernet frames, without relying on broadcast any further. On modern high-performance switches the FDB is typically replicated into a memory located at each input port, and the copy of the FDB associated with each port is the same. This allows each port to route a received frame without waiting to access a shared Forwarding Database. The overall memory requirement becomes significant in situations where the switch has a large number of input and output ports and a large FDB.
Conventional Ethernet networks are connectionless, i.e. no path through the network is pre-established for a frame, or group of frames, corresponding to a traffic flow. Patent Application PCT/GB2005/001332, filed 6 Apr. 2005, describes a way of providing connection-oriented behaviour in Ethernet networks. Connections are provided across an Ethernet network by configuring, via a control plane or management interface, Ethernet switches to map received data frames to particular output ports.